Pinnipeds Hydrodynamic reception

1 pinnipeds

1.1 seals
1.2 sea lions
1.3 species differences in vibrissae

pinnipeds

pinnipeds, including sea lions , seals, use mystacial vibrissae (whiskers) active touch, including size , shape discrimination, , texture discrimination in seals. when used touch, these vibrissae moved forward position , kept still while head moves, moving vibrissae on surface of object. in contrast rodents, move whiskers explore objects. more recently, research has been done see if pinnipeds can use these same whiskers detect hydrodynamic stimuli in addition tactile stimuli. while ability has been verified behaviorally, specific neural circuits involved have not yet been determined.

seals

research on ability of pinnipeds detect hydrodynamic stimuli first done on harbor seals (phoca vitulina). had been unclear how seals find food in dark waters. found harbor seal use whiskers sensory information (due being blindfolded , wearing headphones), respond weak hydrodynamic stimuli produced oscillating sphere within range of frequencies fish generate. active touch, whiskers not moved during sensing, projected forward , remain in position.

to find whether seals follow hydrodynamic stimuli using vibrissae rather detect them, blindfolded harbor seal headphones can released tank in toy submarine has left hydrodynamic trail. after protracting vibrissae forward position , making lateral head movements, seal can locate , follow trail of 40 meters when sharp turns trail added. when whisker movements prevented mask covering muzzle, seal cannot locate , follow trail, indicating use of information obtained whiskers.

trails produced live animals more complex produced toy submarine, ability of seals follow trails produced other seals can tested. seal capable of following center of trail, either following direct path of trail or using undulatory pattern involving crossing trail repeatedly. latter pattern might allow seal track fish swimming in zigzagging motion, or assist tracking weak trails comparing surrounding water prospective trail.

other studies have shown harbor seal can distinguish between hydrodynamic trails left paddles of different sizes , shapes, finding in agreement lateral line in goldfish capable of doing. discrimination between different fish species might have adaptive value if allows seals capture highest energy content. seals can detect hydrodynamic trail produced fin-like paddle 35 seconds old accuracy rate greater chance. accuracy diminishes trail becomes older.

sea lions

more recently, studies on hydrodynamic detection in california sea lion (zalophus californianus) have been done. despite structure of mystacial vibrissae, different of seals, these sea lions can detect , follow trail made small toy submarine. sea lions use undulatory pattern of tracking similar in seals, not perform increased delay before allowed swim , locate trail.

species differences in vibrissae

studies raise question of how detection of hydrodynamic stimuli in these animals possible given movement of vibrissae due water flow during swimming. whiskers vibrate frequency based on swim speed , properties of whisker. detection of water disturbance caused vibrissal movement should overshadow stimulus produced distant fish due proximity. seals, 1 proposal might sense changes in baseline frequency of vibration detect hydrodynamic stimuli produced source. however, more recent study shows morphology of seal s vibrissae prevents vortices produced whiskers creating excessive water disturbances.

in harbor seals, structure of vibrissal shaft undulated (wavy) , flattened. specialization found in true seals. in contrast, whiskers of california sea lion circular or elliptical in cross-section , smooth.

when seals swim vibrissae projected forward, flattened, undulated structure prevents vibrissae bending backward or vibrating produce water disturbances. thus, seal prevents noise whiskers unique whisker structure. however, sea lions appear monitor modulations of characteristic frequency of whiskers obtain information hydrodynamic stimuli. different mechanism might responsible sea lion s worse performance in tracking aging hydrodynamic trail. since whiskers of sea lion must recover characteristic frequency after frequency altered hydrodynamic stimulus, reduce whisker s temporal resolution.